The oxide magnet material typified by the SrO-6Fe2O3, which is a magnet plumbite type hexagonal ferrite and is so-called M-type ferrite, was proposed by J. J. Went et al., (Philips, 1952). Since then, it has been mass-produced and utilized in versatile fields due to its excellent magnetic characteristics and high cost-performance.
Currently, an environmental demands requires the low fuel-cost ratio for automobiles, accordingly the light-weight structure for the main body of the automobiles is promoted. As a result, in order to produce electronic parts with smaller and lighter structure, magnets which serve as major components for these electric parts are urgently needed to be fabricated with much smaller size with higher efficiency.
However, since the degree of magnetization of the above mentioned M-type magnet is small, it has been difficult to obtain the better magnetic properties; for example the maximum energy products--(BH)max--more than 5 MGOe.
In order to provide a ferrite material with larger degree of magnetization than the conventional M-type magnet, it has been proposed that SrO--Fe.sub.2 O.sub.3 which is a principle constituent of the M-type magnet is expanded to the ternary system such as SrO--MeO--Fe.sub.2 O.sub.3 (where Me represents divalent metallic ions such as Co, Zn, or Fe), so that four types (W-type, X-type, Y-type, and Z-type) of more complicated hexagonal ferrite magnets having much stronger ferromagnetism can be fabricated.
Among these, it was found that the W-type magnet has a similar crystalline structure as the conventional M-type magnet and exhibits superior properties such as saturation magnetization of about 10% higher than the M-type magnet and approximately same anisotropic magnetic field. However, the W-type magnet has not been realized.
For example, F. K. Lotgerin et al. proposed the W-type magnets which were consisted of BaO.2(FeO).8(Fe.sub.2 O.sub.3) and SrO.2(FeO).8(Fe.sub.2 O.sub.3) in Journal of Applied Physics (vol.51, p.5913, 1980). However, several drawbacks associated with the proposed magnet were reported; they included (1) a complicated control was required for the sintering atmosphere, and (2) the maximum energy products, (BH)max, for Ba-system magnet was 4.3 MGOe while the (BH)max value for the Sr-system magnet was 3.8 MGOe. Hence these maximum energy product values indicated that these proposed magnets did not possess superior magnetic properties to the conventional M-type magnets.
Moreover, S. Ram et al. reported that the maximum energy products, (BH)max of the Sr.sub.0.9 Ca.sub.0.1 O.2(ZnO).8(Fe.sub.2 O.sub.3) was 2.7 MGOe in IEEE Trans. Magn., vol.1, p.15; 1992. However, this type of magnet was not realized yet.
As a consequence, in order to overcome the problems found in the above articles, it is an object of the present invention to provide a ferrite magnet, and powder for the ferrite magnet as well as production process thereof, by which the W-type magnet can be formulated as SrO.2(FeO).n(Fe.sub.2 O.sub.3), maintaining a similar cost-performance recognized with the conventional M-type magnet and exhibiting an excellent magnetic property such as the maximum energy product value exceeding 5 MGOe.